This invention relates to an apparatus for unloading difficult to fluidize particulate lading from hoppers including industrial bins, overland hopper trucks, intermodal transit hopper type containers and particularly railway hopper cars.
Particulate ladings which readily fluidize, such as plastic pellets are conventionally unloaded from hoppers by means of a fluidizing outlet comprising a permeable membrane. Pressurized air at the unloading site is connected to the outlet and passes through the permeable membrane and upwardly into the outlet to fluidize the lading. The pressurized air and the lading are then metered into a discharge tube and are unloaded from the discharge tube through a transfer pipe into the container to be filled.
However, some ladings do not readily fluidize. Examples include caustic prills, polyvinyl chloride resin, corn starch and cement. If unloading of non-fluidizable particulate ladings is attempted by the fluidizing technique described above, clogging of the outlet generally occurs and the unloading is unsuccessful.
In U.S. Pat. No. 3,019,058 cement is unloaded from a mixing hopper having a discharge tube extending outwardly from the lower portion of the hopper. Air pressure is applied to a control valve located above the top of the hopper. One conduit extends from the control valve to an opening in the top of the hopper. Another conduit extends from the valve to the lower portion of the hopper in line with the discharge tube. A further pair of conduits extend from the control valve to the discharge tube. The control valve may be actuated to apply air under pressure to either one or a pair of the conduits. This arrangement does not include a lading control valve for metering the lading into the discharge tube. However, a lading control valve in a similar pneumatic conveying system is shown in U.S. Pat. No. 2,734,782. The conduit and valve arrangements in each of these patents lack the flexibility to apply air pressure to various portions of the hopper and to the discharge tube in order to maintain efficient unloading rates and avoid clogging and downtime during unloading. For example, with the arrangement in these patents air pressure cannot be simultaneously applied to the top of the hopper, to the discharge tube and to the conduit extending to the lower portion of the hopper in line with the discharge tube.
Also in these patents air is supplied to the upper portion of hopper by a conduit extending outside the hopper which could cause problems with compliance with the Association of American Railroads (AAR) transverse and vertical clearance requirements if such an arrangement were used in a railway hopper car.